The excitable internodal cell of the algae chara australis is exposed to S-band microwave radiation in a temperature controlled exposure chamber to investigate effects upon the resting potential, amplitude, duration, and propagation velocity of the action potential and the excitation threshold. The independent variables investigated include: microwave frequency, pulse-modulation parameters, field intensity, exposure duration, and temperature. The electrical properties are measured by the insertion of microelectrodes into the cell external to the waveguide exposure chamber thus eliminating artifacts due to field pick-up or interference. The primary objective of the research is to compare the effects of continuous wave versus pulse-modulated fields on the electrical activity of an excitable cell model of a neuron. The role of field-induced and nonfield-induced temperature increases will also be determined.